In terms of pure freshness and variety, you should check out Sushi Taro's sushi bar, it's only 6 seats, and you have to reserve by e-mailing them directly. It's $100 per person but you will have your pick of the most variety of seafood offered in the DC area, including fresh fish flown in from Japan. It's actually a 10 course omakase but how much sushi and sashimi you want is up to you.